The invention relates to improvements in fluid-operated cylinder-and-piston assemblies in general, and more particularly to assemblies known as master cylinders. A master cylinder can be utilized, for example, in a motor vehicle where it can form part of a device such as a hydraulic brake or clutch.
As a rule, a master cylinder comprises a cylinder or housing defining a chamber for a reciprocable piston which can displace a column of liquid to thus actuate a brake or a clutch, e.g., by way of a so-called slave cylinder. xe2x80x9cModern Automotive Technologyxe2x80x9d (authored by James E. Duffy and published by The Goodheart-Willcox Company, Inc. of Tinley Park, Ill.) defines a master cylinder for a brake pedal assembly as a foot-operated pump that forces liquid into the brake lines and wheel cylinders. Its basic functions are to develop pressure, causing the wheel cylinder pistons to move toward rotors or drums; to help equalize the pressure required for braking after all of the shoes or pads produce sufficient friction; to keep the system full of fluid as the brake linings wear; and to maintain slight pressure to keep contaminants (such as air and/or water) from entering the system.
A master cylinder can be assembled with a brake pedal or with a clutch pedal to form part of a module which is ready to be installed in a motor vehicle, e.g., to apply brakes to the wheels or to engage or disengage a friction clutch. In many master cylinders, the brake pedal or clutch pedal is linked to a piston rod having a free end provided with a spherical head which is connected to and can swivel relative to the piston in the housing of the master cylinder. The module can be installed on a wall, e.g., between the space for the prime mover and the driver compartment. The piston can displace a column of liquid in order to cause the piston of a slave cylinder to expel liquid from the housing of the slave cylinder or to permit liquid to reenter the housing.
Reference may be had, for example, to published German patent application Ser. No. 196 08 132 A1 which describes and shows a conventional master cylinder. The latter comprises a housing made of a plastic material and defining a chamber for a plastic piston. The piston rod of the master cylinder has a spherical head which is form-lockingly connected with the piston. To this end, the piston is provided with a socket having a recess bounded by a concave surace and serving to receive the head of the piston rod (reference may be had to FIG. 3 of the German published application). The piston is slotted axially in the region of the head of the piston rod so that the head can be readily introduced into the socket. A firm swiveling connection between the head of the piston rod and the piston is established by a sleeve which is slipped onto the slotted part of the piston so that the latter snugly surrounds the head and prevents separation of the spherical head from the piston.
A drawback of such master cylinders is that at least the slotted end of the piston and/or the head of the piston rod (also called push rod) must be made of a highly elastic material in order to permit the head of the piston rod to enter the cavity of the socket in the piston. As a rule, the head of the piston rod and/or the piston must be made of an elastomeric material, particularly a thermoplastic material which permits adequate deformation of the head and/or of the adjacent end of the piston and to thus permit insertion of the head into its socket. In many instances, the thermal expansion coefficient of a thermoplastic material is very high and actually too high because the stability of the piston is not sufficient for the intended purpose. In other words, the stability of the entire master cylinder is unsatisfactory for the intended purpose e.g., for use in a brake system or in combination with a clutch in the power train of a motor vehicle.
The manner in which an electronically controlled or operated master cylinder can regulate the operation of a clutch by way of a slave cylinder in the power train of a motor vehicle is described and shown, for example, in commonly owned U.S. Pat. No. 5,725,456 granted Mar. 10, 1998 to Robert FISCHER et al. for xe2x80x9cMETHOD OF REGULATING THE OPERATION OF A TORQUE TRANSMISSION APPARATUSxe2x80x9d. The disclosure of the commonly owned priority application Ser. No. 197 52 076.6, as well as the disclosure of each U.S. and foreign patent and patent application identified in the specification of the present application are incorporated herein by reference.
An object of the present invention is to provide a master cylinder wherein the connection between the piston and the piston rod is more reliable than in heretofore known master cylinders.
Another object of the invention is to provide a relatively simple and inexpensive but higly reliable swivel joint between the piston and the spherical head of the piston rod or push rod in a master cylinder which is suitable for use in the power train between the prime mover (such as an internal combustion engine) and the wheels of a motor vehicle.
A further object of the invention is to provide a novel and improved arrangement which couples a female part to a spherical male part in such a way that the force with which a separation of the male part from the female part is opposed invariably exceeds a preselected lower threshold value irrespective of the orientation of male and female parts relative to each other.
An additional object of the invention is to provide a novel piston for use in the above outlined master cylinder.
Still another object of the invention is to provide a novel and improved reliable (but separable, if and when necessary) joint between the piston and the piston rod in the chamber of a housing forming part of a master cylinder for use in conjunction with the braking system or with a clutch in the power train of a motor vehicle.
A further object of the invention is to provide a master cylinder adapted to be utilized as a superior (e.g., longer-lasting) substitute for conventional master cylinders which are presently employed in the power trains of motor vehicles.
An additional object of the invention is to provide a master cylinder which constitutes a less expensive, more reliable, more compact and more readily assemblable and/or disassemblable substitute for presently known master cylinders.
Another object of the invention is to provide a novel and improved method of connecting the spherical head of a piston rod or push rod with the piston of a master cylinder.
Still another object of the invention is to provide a module wherein the piston and the spherical head of a piston rod are assembled with each other in a novel and improved way with freedom of swivelling movement relative to each other and in a condition of readiness for installation in the housing of a master cylinder for use in conjunction with the braking system or with a friction clutch in the power train of a motor vehicle.
A further object of the invention is to provide a module which forms part of a master cylinder and can be installed in the housing of a master cylinder in a simple and reliable manner, be it in conjunction with one or more brakes or in conjunction with a friction clutch.
An additional object of the invention is to provide a highly compact and lightweight master cylinder for use in the power train of a motor vehicle.
The invention is embodied in a cylinder and piston assembly, particularly in a master cylinder, which comprises a housing defining a chamber, a piston which is reciprocable in the chamber, a reciprocable piston rod including a spherical head extending into the chamber into engagement with one end of the piston, and means for articulately coupling the head to the one end of the piston. The coupling means includes a first section which engages the piston rod and a second section which is affixed to the piston.
The piston is or can be made of a plastic material, and at least a portion of the coupling means can consist of a metallic sheet material, i.e., such portion of the coupling means can constitute a suitably deformed sheet metal blank.
In accordance with a first embodiment of the invention, the first section of the coupling means can constitute a portion of a hollow sphere which surrounds and bears upon a portion of the head and has a central opening remote from the second section of such coupling means and surrounding a portion of piston rod. The piston rod further includes an elongated part having an end connected to (e.g., of one piece with) the spherical head; the first section of the coupling means surrounds the head at the end of the elongated part of the piston rod, and the second section can include a tubular portion surrounding the one end of the piston. The one end of the piston can be provided with a circumferentially complete or multiple-section external groove, and the second section of the coupling means can include at least one projection which extends into the groove to hold the coupling means against axial movement relative to the piston and/or vice versa. The first section of the coupling means can be provided with axially parallel slots alternating with prongs or arms which bear upon and bias the spherical head against the one end of the piston. The first section of the coupling means can be provided with an annular end portion which surrounds the aforementioned central opening and has a convex internal surface which is maintained in substantially linear contact with the head of the piston rod.
In accordance with another embodiment of the invention wherein the one end of the piston surrounds at least a major portion of but normally the entire head of the piston rod, the coupling means can include a substantially cup-shaped second section which comprises a tubular portion surrounding the one end of the piston and an annular end wall which surrounds the piston rod at the head. The one end of the piston has an external groove and the tubular portion of the second section has at least one projection extending into the groove. The first section of the coupling means is confined in the second section and includes a sleeve which reacts against the end wall of the second section and bears upon the head of the piston rod.
In accordance with still another embodiment of the invention, the coupling means can include or constitute a clip made of metallic wire or the like. For example, the first section of a clip which constitutes the coupling means can include prongs which abut the end face at the one end of the piston and engage the head of the piston rod, and the second section of such clip can include links which connect the prongs and are received in an internal groove of the one end of the piston. The first section of such clip can include two prongs and the second section can include two links which are received in the aforementioned groove by snap action to urge the two prongs against the end face of the one end of the piston and against the head of the piston rod.
Alternatively, a clip which constitutes or forms part of the coupling means can comprise two legs which flank the piston rod and bear upon the head to bias the head into a complementary socket in the one end of the piston. The second section of the coupling means embodying or constituting the clip is anchored in the one end of the piston by snap action. The one end of the piston can be provided with radially extending slots for the second section of the clip. The latter can be U-shaped and its legs can be provided with arcuate median portions which engage the head of the piston rod. The second section of such clip can include the first and second ends of the aforementioned legs and a web which connects the first ends of the legs to each other. The second ends of the legs can be provided with extensions in the form of teeth or the like which are received in complementary recesses machined or otherwise provided in the one end of the piston.
In accordance with a further embodiment of the present invention, the one end of the piston is provided with a channel (e.g., with an axial bore or hole) which receives the head of the piston rod. The coupling means is at least partially confined in the channel and includes a sleeve which surrounds the piston rod adjacent to the head of the latter; the sleeve has a radially outwardly extending first end portion which constitutes the second section of the coupling means and is recessed into the piston. An inwardly extending second end portion of the sleeve bears against the head of the piston rod and acts as the first section of the coupling means.
It is also possible to design the master cylinder in such a way that the head of the piston rod is at least partially but preferably fully confined in the one end of the piston and that the second section of the coupling means abuts the end face at the one end of the piston. The first section of such coupling means is or can be provided with prongs which are of one piece with the second section, which are anchored in the one end of the piston and which abut the head of the piston rod. The prongs can further serve as a means for centering the first section of the coupling means in the axial channel of the piston.
The first section of a further embodiment of the coupling means can be confined in the second section and can include a sleeve which reacts against the second section and bears upon the head of the piston rod to bias the head into an internal socket provided in the one end of the piston. At least a portion of such coupling means can consist of a plastic material and its first section can be provided with a concave surface which abuts and is complementary to a convex external surface of the head.
The first section of a modified coupling means can be of one piece with the second section; the first section of such coupling means abuts an end face at the one end of the piston and has a concave seat which surrounds the head of the piston rod. The second section of the coupling means has prongs which are externally adjacent the one end of the piston and have projections extending into complementary recesses of the one end of the piston.
In accordance with a further embodiment, the coupling means can comprise an elongated body which can resemble a bar confined in the one end of the piston. The second section of the coupling means constitutes a first part of the bar and is anchored in the piston, and the first section of the coupling means constitutes a second part of the bar and is anchored in the head of the piston rod. The one end of the piston is provided with internal tongs which engage the second section of the bar by snap action.
The one end of the piston can have a diameter smaller than that of an adjacent median portion of the piston. A portion of the coupling means is or can be mounted and configurated in such a way that its surrounds the one end of the piston; such portion of the coupling means can include or constitute the second section.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved master cylinder itself, however, both as to its construction and the mode of assembling its parts, together with numerous ad-titional important and advantageous features and attributes thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawings.